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Neighbors Corvette is kicking my rear...need some help.

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nocooler:
So I've been helping the neighbor try to diagnose his issues.


The major glaring issue I see is TPS volts climb to 1.8v at WOT according to the scanner. New sensor didn't help, connector housing was cracked so I de-pinned it and used a new connector. I have 5v across the ground and reference at the sensor. I have like 4.8v checking across the reference and signal wire. All within spec
I've traced the wires from the TPS to the firewall and they look good. I tested the voltage at the computer and it sees 2.3v @ WOT at the connector, so within a half a volt of what the scanner shows. The harness looks untouched under the dash the pcm connectors were clean.
The wiring diagram (http://chevythunder.com/198689_f__y_body_1227165.htm) shows that the TPS shares a ground with the MAT and CLT sensors. If I test across the wires at the MAT is get 5v, at the coolant sensor 4v. The CLT wires look good to the firewall, the MAT I can't trace without pulling the plenum off. The scanner show logical temp numbers for the MAT and CLT sensors when plugged in and unplugged the scanner shows -31f or whatever the lowest value is.
Scanner doesn't show ecm voltage.
I am getting a code for the for the low TPS and the MAT sensor high air temps. Scanner shows CLT and MAT are reading right.
I'm thinking it's probably a ground issue - I can't get to the grounds at the back of the heads, but that is where I am leaning. Hopefully they are accessible from the bottom. The other possibility is when the exhaust shop welded the exhaust they didn't disconnect the battery and damaged the ecm - but that's more of a long shot imo.
Any other ideas? 

nocooler:
This almost seems like what it was doing - http://www.gearhead-efi.com/Fuel-Injection/showthread.php?6793-165-ECM-weird-CTS-and-TPS-readings
Maybe I should have him pickup a used computer?

Steve Wood:
My first thought was bad ground, but, after reading that link, I guess another ecm is within reason.  Hate to buy stuff so is there anywhere he could borrow one?

nocooler:
I hate to buy stuff too - I don't know anyone else that has one we could borrow.
https://www.autozone.com/engine-management/engine-control-computer/blue-streak-engine-control-computer-ecc7165/10450_50404_6207
This seems reasonably priced.

Steve Wood:
Yes, it is.  Maybe you can take it back if it does not fix the problem?  Or, for $73, it could be a back up if I had to justify it.

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